a stained anus, kinda browner than you think it should be...maybe even a dingle-berry or two present. Rhymes with anus.

Biff: Hey Blaine...that chick I banged last was awesome. But, when she bent over and pulled her panties off, I saw her stainus! It was rotten. But, I did her anyways.
Blaine: Did your tool smell like ass?